In the past, pneumatic motors for rock drills and the like have been provided wherein the hammer piston includes reduced-diameter portions extending axially on opposite sides of an enlarged central piston portion. The reduced-diameter portions include reduced area sections which act as inlet valve means for valving motive air to the piston head from both ends of the cylinder. One example of such a pneumatic motor can be found by reference to U.S. Pat. No. 1,264,217, issued Apr. 30, 1918.
Pneumatic motors of the aforesaid type usually have bores extending along the cylinder wall for connecting the inlet valve means at one end of the cylinder to the other and for connecting both valve means to a fluid pressure source. As a result, the machining and assembly of such pneumatic motors are relatively expensive and complicated.